The present invention relates to a printer with a tonality correction capability and more particularly to a printer with a tonality correction capability and allowing even the user of the printer to adjust the variation of tonality ascribable to a difference in the type of the printer and aging.
A printer, particularly a copier, with a semiautomatic tonality correction capability, i.e., a method and an apparatus for printing a test pattern on a recording medium, reading it with a scanner, and automatically adjusting tonality to a target has been proposed in the past. Japanese Patent Laid-Open Publication No. 5-114962, for example, discloses a printer storing a test pattern and reading an image pattern based on the test pattern with image reading means thereof. Data listed in an image signal conversion table are corrected in accordance with the image pattern read by the image reading means, so that quality image can be stably output even when the output variation characteristic varies due to, e.g., the deterioration of image forming means. Japanese Patent Laid-Open Publication No. 9-107478 teaches a printer capable of correcting a signal representative of a pattern formed on a recording medium with data representative of the background of the medium. This printer copes with an occurrence that the output value of a scanner or similar image reading device varies. Further, Japanese Patent Laid-Open Publication No. 9-23340 proposes an image reading device capable of compressing image data existing on the rear of a document by using a method different from a method for compressing image data existing on the front of the same document.
None of the above conventional schemes, however, takes account of a plurality of tonality processing methods customary with a printer and selectively used in accordance with a memory capacity, among others. As a result, even if tonality is corrected without an output device executing tonality processing, i.e., only by the print tonality ability of the engine, high density portions included in an output undergone tonality processing are often smeared out. More specifically, when tonality processing is not executed, tonality is rendered by a single dot sequentially increasing in size or in density and adjusted to a target in such a manner as to continuously vary. However, when tonality is rendered by, e.g., dither processing after the above dot adjustment, density stops varying at a certain point. That is, when a dot diameter of a certain level exceeds a preselected diameter, large dots surrounding a small dot fill up the small dot, depending on a pattern. As a result, image density does not vary even if the diameter of the small dot is increased.
In light of the above, there may be used a method that variably corrects only the tonality of a condition not subjected to correction, and reads a fixed difference between it and a corrected condition out of a correction table. Even this method, however, cannot sufficiently absorb the variation of an image formed by a sophisticated process and ascribable to a difference in the type of a printer and aging.
Further, for a given level represented by identical density output from a densitometer, the output of a scanner often varies due to the scanner characteristic, depending on the tonality processing method.
Moreover, when the user of the printer is not satisfied by the above general tonality correction, tonality correction is executed a plurality of times in accordance with the tonality correcting method. This, however, wastes papers and other supplies, manual operations and cost necessary for tonality correction.
It is therefore an object of the present invention to provide a printer capable of adequately and simply adjusting tonality in accordance with a desired tonality correcting method and allowing even the user of the printer to adjust the variation of tonality ascribable to a difference in the type of a printer and aging.
A printer of the present invention includes an image reading section for reading an image. An image writing section processes image data input thereto to thereby write an image for forming an image. An image forming section forms an image with any one of a plurality of tonality processing methods that form data written by the image writing section. A test pattern forming section forms a particular test pattern for each of the plurality of tonality processing methods.
The image reading section reads the test pattern formed by the test pattern forming section in accordance with the tonality processing method. Data representative of the test pattern are compared with target data for thereby executing tonality correction matching with the tonality processing method.